Dual Channel Temperature Sensor

and Over Temperature Alarm

ADT7481

Rev. 0

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FEATURES

1 local and 2 remote temperature sensors

0.25°C resolution/1°C accuracy on remote channels

1°C resolution/1°C accuracy on local channel

Extended, switchable temperature measurement range 0°C

to 127°C (default) or –64°C to +191°C

2-wire SMBus serial interface with SMBus ALERT support

Programmable over/under temperature limits

Offset registers for system calibration

Up to 2 over temperature fail-safe THERM outputs

Small 10-lead MSOP package

240 μA operating current, 5 μA standby current

APPLICATIONS

Desktop and notebook computers

Industrial controllers

Smart batteries

Automotive

Embedded systems

Burn-in applications

Instrumentation

GENERAL DESCRIPTION

The ADT74811 is a 3-channel digital thermometer and under/

over temperature alarm, intended for use in PCs and thermal

management systems. It can measure its own ambient temperature

or the temperature of two remote thermal diodes. These thermal

diodes can be located in a CPU or GPU, or they can be discrete

diode connected transistors. The ambient temperature, or the

temperature of the remote thermal diode, can be accurately

measured to ±1°C. The temperature measurement range defaults

to 0°C to +127°C, compatible with ADM1032, but can be

switched to a wider measurement range from −64°C to +191°C.

The ADT7481 communicates over a 2-wire serial interface

compatible with system management bus (SMBus) standards.

The SMBus address of the ADT7481 is 0x4C. An ADT7481-1

with an SMBus address of 0x4B is also available.

An ALERT output signals when the on-chip or remote

temperature is outside the programmed limits. The THERM

output is a comparator output that allows, for example, on/off

control of a cooling fan. The ALERT output can be reconfigured

as a second THERM output if required.

FUNCTIONAL BLOCK DIAGRAM

11-BIT A-TO-D

CONVERTER

RUN/STANDBY

BUSY

REMOTE 1 AND 2 TEMP

OFFSET REGISTERS

STATUS REGISTERS

INTERRUPT

MASKING

CONFIGURATION

REGISTERS

REMOTE 1 AND 2 TEMP

HIGH LIMIT REGISTERS

REMOTE 1 AND 2 TEMP

LOW LIMIT REGISTERS

REMOTE 1 AND 2 TEMP

THERM LIMIT REGISTER

LOCAL TEMPERATURE

HIGH LIMIT REGISTER

LOCAL TEMPERATURE

LOW LIMIT REGISTER

LOCAL TEMPERATURE

THERM LIMIT REGISTER

ONE-SHOT

REGISTER

ADDRESS POINTER

REGISTER

CONVERSION RATE

REGISTER

REMOTE 1 AND 2 TEMP

VALUE REGISTERS

LOCAL TEMPERATURE

VALUE REGISTER

ON-CHIP TEMP

SENSOR

ANALOG

MUX

EXTERNAL DIODES OPEN-CIRCUIT

SMBUS INTERFACE

ADT7481

7

8

3

2

10

4

1

6

9

GND

SDATA

SCLK

THERM

8

D1+

D1–

D2+

D2–

ALERT/THERM2

Figure 1.